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%I #36 Jan 09 2020 14:13:19
%S 1,2,4,7,1,6,2,9,7,6,6,7,9,2,6,1,7,4,2,1,1,2,4,7,1,6,2,9,7,6,6,7,9,2,
%T 6,1,7,4,2,1,1,2,4,7,1,6,2,9,7,6,6,7,9,2,6,1,7,4,2,1,1,2,4,7,1,6,2,9,
%U 7,6,6,7,9,2,6,1,7,4,2,1,1,2,4,7,1,6,2,9,7,6,6,7,9,2,6,1,7,4,2,1,1,2,4,7,1
%N a(1) = 1, a(n+1) = (a(n) + n) mod 10.
%C First row of array shown below.
%C a(n) = most significant digit of A062273(n).
%C Period 20: repeat [1, 2, 4, 7, 1, 6, 2, 9, 7, 6, 6, 7, 9, 2, 6, 1, 7, 4, 2, 1]. - _Peter M. Chema_, Feb 12 2017
%F a(n) = A008954(n-1) + 1.
%F a(n) = A000124(n) mod 10. - _Peter M. Chema_, Feb 11 2017
%F From _Chai Wah Wu_, Jan 09 2020: (Start)
%F a(n) = a(n-5) - a(n-10) + a(n-15) for n > 15.
%F G.f.: x*(-x^14 - 2*x^13 - 4*x^12 - 7*x^11 - x^10 - 5*x^9 - 5*x^7 - 5*x^5 - x^4 - 7*x^3 - 4*x^2 - 2*x - 1)/(x^15 - x^10 + x^5 - 1). (End)
%e 1 2 4 7 1 6 2 9 7 6 6 ...
%e 3 5 8 2 7 3 0 8 7 7 ...
%e 6 9 3 8 4 1 9 8 8 ...
%e 0 4 9 5 2 0 9 9 ...
%e 5 0 6 3 1 0 0 ...
%e 1 7 4 2 1 1 ...
%t a = {1}; Do[AppendTo[a, Mod[a[[n - 1]] + n - 1, 10]], {n, 2, 120}]; a (* _Michael De Vlieger_, Feb 13 2017 *)
%o (PARI) a(n)=if(n==1,return(1));(a(n-1)+n-1)%10
%o for(n=1,50,print1(a(n),", ")) \\ _Derek Orr_, Feb 26 2017
%Y Cf. A061352, A061353.
%Y Cf. A062273, A077577, A077578.
%Y Cf. A000124.
%K base,nonn,less
%O 1,2
%A _Amarnath Murthy_, May 06 2001
%E Better description and more terms from Larry Reeves (larryr(AT)acm.org), May 08 2001
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